This invention relates to the treatment of neoplastic diseases stemming from oncogenesis and collectively known as cancer. More particularly, it relates to a novel vaccine and method for using same in the therapy of malignant neoplasms which afflict mammals, including man, such as sarcomas, the carcinomas, and the hematologic cancers, through the activation or stimulation of the body's immune system to achieve remission and destruction of cancerous tissue. While the term "vaccine" is understood generally to means a bacteriological or viral-derived agent, it is used herein more broadly to encompass substances prepared in accordance with the invention for activating the body's immune response.
The more advanced forms of animal life have the ability to produce substances known as antibodies when exposed to certain agents called antigens. The production of antibodies resulting from the introduction of an antigen into the body is called the "immune response"; its purpose is to protect the body against potentially harmful substances or organisms. A characteristic feature of antibodies is that, for all intents and purposes, they will only combine with the particular antigen which stimulated their production, i.e., a particular antibody will combine only with a specific antigen. Any material may be an antigen. For example, an antigen may be a metal, lipid, protein, carbohydrate or a combination of two or more of these broad classes of materials. Apart from its chemical composition, an antigen can be a whole molecule, a portion of the surface of a molecule or a portion of the surfaces of a group of molecules. On the other hand, all antibodies are individual discrete molecules belonging to a class of proteins known as globulins and as such all antibodies have the same fundamental molecular structure although they do vary in size depending on the molecular weight of their fundamental components.
Although antibodies all have basically the same gross molecular structure, they vary in subtle but distinct ways much as the notches of different keys vary in almost innumerable ways. It is this variation which enables a particular antibody to distinguish between innumerable antigens and to combine only with the specific antigen which stimulated the production of the antibody, much in the same way that a key will fit only its own particular lock. Thus, a particular sequence of "notches" will be found only in a population of antibody molecules which combine with a specific kind of antigen. If the sequence varies only slightly the antibody will not combine with the antigen in question. The current state-of-the-art with respect to what is known about the immune response is exemplified in the article by M. D. Cooper et al. entitled "The Development of the Immune System" appearing in Scientific American, pages 59-72 (November 1972).
Antibodies are either "cellular" or "humoral" depending upon whether they are attached to the surfaces of certain white corpuscles or exist unattached as free individual molecules, respectively. After an antigen is introduced into the body there is a delay of from two to ten days before the appropriate antibodies are manufactured and secreted or discharged into the blood-stream and certain body secretions. (Undoubtedly, antibodies are manufactured more rapidly than this, however, the elapsed time before they can be detected probably reflects the sensitivity of current analytical techniques). The number, type, and combining affinity of the antibodies produced determine the degree or extent of cellular or humoral immunity against the specific antigen in question. As a general rule small antigens stimulate the production of humoral antibodies whereas large antigens, such as those fixed to surfaces or clumps of antigen carriers, lead to the production of cellular antibodies. This distinction is important to an understanding of the role of the immune response in cancer.
The first step in the immune response to a harmful agent is the detection of antigens which are not normally present in the body. The body, of course, contains innumerable antigens of its own. Therefore, the antigens which must be detected are "non-self" or foreign antigens. Detection of foreign antigens is accomplished by constantly monitoring the antigens on all of the cells and molecules within the body. This monitoring function is performed largely by certain kinds of white cells which continuously explore all parts of the body via the circulatory system. When an antigen is found the monitoring cells are "programmed" to respond only if the antigen is foreign to the body, i.e., does not belong there. When a foreign antigen is detected, the monitoring cells responsible for such detection respond by initiating a series of events which ultimately give rise to the production of cellular or humoral antibodies which then combine with the antigen. This antigen-antibody combination usually destroys the harmful biologic effects of the source of the antigen. In this way the body protects itself against toxins and invading microorganisms (viruses, bacteria and parasites). As a general rule, humoral anti-bodies are produced if the antigen is part of a toxin, an individual molecule, virus or bacterium, whereas cellular anti-bodies are produced if the antigen is part of a multi-cellular organism such as a large parasite or a transplant of a foreign tissue. The concept of the "immune response" has been employed in the past for the prevention and treatment of several dreaded infectious diseases, including smallpox and polio. In particular, the prevention or treatment of disease by means of promoting or stimulating the appropriate immune response is known as "immunization" or "immunotherapy", respectively. The general state-of-the-art of immunology which provides the scientific basis for immunotherapy is contained in the following references: M. C. Raff, "Cell-Surface Immunology", Scientific American, pages 30-39 (May, 1976); D. T. Rowlands, et al., "Surface Receptors in the Immune Response", New Eng. J. Med., 293 26-32 (1975); and T. Rajan, "The Immune System", N.Y. State Med. J 1077-1085 (July, 1976).
In addition to protecting the body against harmful influences invading it from without, the immune response appears for the following reasons to be responsible for protecting the body from certain harmful influences arising from within, namely, the various neoplastic diseases known collectively as "cancer".
First, every cancer which has been adequately tested has been found to possess on the surface of its cells antigens which are foreign to the host. See, for example, the article by R. E. Pollack et al. entitled "The Cell Surface and Malignant Transformation", Ann. Rev. Med., 25, 431-446 (1974). These diseases are characterized by the unremitting multiplication of the cancerous cells without the restraints which govern the "social behavior" of normal cells. As a result, cancer cells push into and invade normal adjacent cells, leading to pain and the destruction of the normal cells. If the normal cells under attack comprise a vital organ, death will often result. In addition, normal cells are selectively adhesive to other normal cells of the same type and through this adherence are able to build up complex organ systems. Cancer cells tend not to adhere to each other, a situation favoring "metastasis" whereby cancer cells break away from the parent cancer tissue and become distributed to other parts of the body where they multiply and invade other normal cells. These resultant metastases often cause pain or death. This abnormal behavior of cancer cells is believed to be due at least in part to cell surface characteristics which are not present in normal cells. The surfaces of normal cells send a signal to the cell nucleus when cell multiplication must cease, as in the repair of a skin wound, a phenomenon known as "contact inhibition". Cancer cell surfaces apparently do not send such signals, as a result of which the cancer cells continue to multiply, piling upon each other and invading normal cells. The factors responsible for these differences between the cell surfaces of normal and cancer cells are believed to comprise, at least in part, the antigens of the cancer which are regarded as "foreign" by the host.
Second, the body possesses the ability to destroy via the immune response a vast number of cells, and indeed, an entire organ. This is seen in the rejection of a kidney or heart transplant. Thus, the destructive capability of the immune response is in some instances immense and, if properly channeled, is presumably capable of destroying newly arising cancers.
Third, the ability of the immune response to destroy large numbers of cells appears on the phylogenetic scale at the same point as cancer. In general terms, when cells multiply there are always a small number thereof which will be abnormal. When the abnormality of one of these cells is manifested in the acquisition of cell surface characteristics which result in unremitting multiplication, invasion of the body, and widespread distribution of daughter cells, the abnormal cell will produce a potentially lethal cancer. As organisms through evolutionary processes have become more complex the likelihood of cancer cells evolving has also increased. Eventually, with increasing complexity of the organism, the frequency of cancer cells appearing became so great that the organism was unable to mature and reproduce. Then in order for evolution to proceed further, a mechanism was needed to protect the organism from the cancer cells constantly appearing within. Evolution apparently developed such a mechanism which is the type of immune response seen in the rejection of a transplanted organ such as a kidney or heart. This type of immune response did not arise to thwart the transplantation surgeon but rather to protect the body against cancer. As mentioned earlier, this type of immune response leads to cellular immunity or cellular immune response as distinct from humoral immunity or humoral immune response.
Finally, the incidence of cancer rises markedly when the cellular immune response is weak, whether the weakness results from inherent defects of the host's immune system or from destruction or suppression of the immune system by drugs, surgery or radiation. This increased incidence of cancer is seen in experimental animals and in humans. In humans, suppression of the immune response by drugs in order to assure the survival of a transplanted kidney has been found to lead to an incidence of cancer 2,000 times greater than that seen in the normal population. This suggests that the degree of suppression necessary to prevent the immune response from destroying the transplanted kidney also weakens the immune response against the abnormal, potentially cancerous cells constantly appearing in the body so that inevitably the frequency of clinical cancer becomes greater. When the immune suppressive therapy is stopped the newly arisen cancer usually disappears.
The relationship between the immune response and cancer leads to the concept of immunologic surveillance, which was initially proposed by Burnet (see F. M. Burnet, "Immunological Surveillance", Pergamon Press, New York 1970 and by Thomas (see L. Thomas in "Cellular and Humoral Aspects of the Hypersensitive State", H. S. Lawrence, ed., p. 259 (Holber, New York 1959)). According to this concept the special white cells, which are responsible for detecting antigens foreign to the host, by constantly monitoring all cells and substances of the body, detect any newly appearing cells having characteristics of cells destined to form cancers. After detection these cells are destroyed by an immune response, and in this manner the body is protected against cancer. Such an immunologic surveillance is performed by the same cellular components responsible for the immune response against, and the rejection of, transplanted organs. Furthermore, the cancer-specific antigens detected by immunologic surveillance are quite similar to the transplantation antigens responsible for the immunologic rejection of transplanted organs. Both cancer-specific and transplantation antigens contain carbohydrates and both are present on the surfaces of their respective cells. Both can stimulate the production of cellular immunity. Indeed, the reason for the existence of immunologic surveillance and its powers were not fully appreciated until its suppression became recognized as essential for the survival of transplanted kidneys. As mentioned earlier, it is the cellular type of immunity which is believed to be evoked against cancer cells which are detected by immunologic surveillance. Likewise, a cellular type of immune response is directed against transplanted organs.
As also mentioned earlier, malignant cells are constantly appearing among the various cell populations within the body. The body's cells must constantly be replenished to make up for losses due to injury or senescence. This is accomplished by cells multiplying when necessary. Each time a cell multiplies there is a finite, albeit slight, chance of an error occurring in its complex machinery for multiplication. Consequently, there is a base level of error which cannot be reduced further, reflecting the extreme complexity of the cellular machinery in operation when a cell multiplies. The incidence of this error, however, can be increased by hereditary factors as well as by environmental factors such as radiation, viruses, and chemicals. While these factors increase the incidence of malignant cells, only a few such cells ever survive immunologic surveillance to multiply and create the disease state of cancer. Evolutionary forces dictate that only those cells that have evolved means for evading immunologic surveillance will develop into cancer. Thus, while the failure of immunologic surveillance may be regarded as the single cause of cancer, there are many factors (viral, carcinogenic, radiative) which increase the frequency with which immunologic surveillance must operate successfully if the host is to be protected against the emergence of cancer. When an error does occur, the two daughter cells produced are often not true replicas of the parent cell. Occasionally the error of replication produces a cell which continues to multiply when the need for multiplication no longer exists. This cell and its daughter cells are now malignant and grow to form a cancer. However, as explained earlier, these malignant cells are usually, recognized by means of their cancer-specific antigens which are foreign to the host and they are normally destroyed by an immune response. The question of how cancers arise despite their possession of antigens foreign to the body and despite immunologic surveillance by the host remains one of the great unsolved problems confronting medical science.
Of the malignant cells constantly developing only a very few survive to become cancers. It is not sufficient for a cell to be abnormal merely with regard to being able to multiply increasingly in order to become a cancer. It must also be abnormal to the extent of acquiring devices or mechanisms capable of enabling it to survive immunologic surveillance. Only a few of these devices are known at present. For instance, cancer cells have long been known to possess on their surfaces proteolytic enzymes potentially capable of producing small fragments of cancer antigens. These small fragments of cancer antigens are more likely to stimulate the production of humoral antibodies than cellular antibodies. In certain instances, although these humoral antibodies do combine with the cancer cells, they do not destroy them. Indeed they appear to coat and protect the cancer cells from destruction by cellular antibodies. In this way, the small fragments of cancer antigens are able to blind the special white cells which look for antigens much as small pieces of tinfoil can blind radar.
Finally, the ability of cancer cells to survive immunologic surveillance may depend upon their ability to secrete substances which inhibit the recruitment of other types of cells when antibodies complex with antigen. Normally, antigen antibody complexes can release substances which attract other types of cells necessary for the rapid immunologic destruction of the cancer cells possessing the antigen. It is conceivable that the participation of these other types of cells could be inhibited by substances secreted by the cancer cells. Thus, a vigorous detection and immunologic destruction of the cancer would not occur.
The treatment of cancer by immunotherapy, pursued earlier in this century with great hope and zeal, began with the discovery that animals could survive and reject lethal transplants of cancer if they were first pre-immunized with small, non-lethal transplants of cancer tissue. However, this approach was unsuccessful in treating human cancer. It was later learned that the success of the animal experiments was solely due to histocompatability differences between the cancer tissue donor and the recipient animals, for immunization against the cancer could be achieved just as readily by immunizing the animal with non-cancerous tissue from the animal supplying the cancer. In other words, there was no evidence that cancer-specific antigens, i.e., antigens unique for the particular cancer, existed. Immunotherapy of cancer, lacking a rationale, fell into disrepute. See W. H. Woglom, The Cancer Review, 4, 129-214 (1929). In the 1950's, however, highly inbred mouse strains became available. All members within a given strain possess the same antigens and no others, and it was proved unequivocally that cancer antigens, albeit very weak, do indeed exist. These are antigens which are located on the cancer cell surface, are distinctive for the particular cancer, and are not found in the non-cancerous tissues of the host. Unfortunately, these antigens tend to lose their ability to stimulate a cancer-destructive type of immune response when the cancer dies, making the preparation of an effective conventional vaccine for the immunotherapy of cancer difficult.
Four approaches to cancer immunotherapy utilizing the cancer-specific antigen are currently being evaluated. It is well-recognized that extracts of cancer cells per se have no therapeutic value. However, if cancer cells are treated with the enzyme neuraminidase, which strips off carbohydrate material from the cell surface, the cancer cell antigens in experimental animals appear more capable of stimulating an immune response of value in cancer therapy. Presumably, the action of neuraminidase removes substances masking the cancer antigen. This approach has not been of any demonstrated value in treating cancer in humans. Another approach is to complex the cancer antigens with a strong antigen of another type, the hope being that the immune response elicited against the strong antigens will also produce antibodies specific for the weaker cancer antigens. This approach has been of little success to date, but it may explain some of the small success of another approach to cancer immunotherapy, which utilizes the vaccine of Bacillus Calmet-Guerin (BCG). This vaccine, which normally is injected in order to immunize humans against tuberculosis, also has the property of increasing in a non-specific way the immune response against a variety of antigens when these antigens are administered simultaneously (but not necessarily at the same location) with the BCG vaccine. This approach is being evaluated in various laboratories for use in the treatment of leukemia. It does appear to increase somewhat survival in these diseases. BCG is also being used to treat certain selected cases of malignant melanoma. Some dramatic remissions and even cures have been reported when the BCG is injected directly into the melanoma nodule. Finally, in the fourth approach, there have been a few isolated cases of remission of malignant melanoma following injection of the patient with serum from another patient already in remission from malignant melanoma. Presumably, the donor-patient serum possesses antibodies against the cancer-specific antigens of the patient to be treated.
Other types of immunotherapy include the use of transfer factor or mobilizing factor and of RNA of white cells involved in the immunologic rejection of cancer. While attractive in theory, none of these approaches has proved to be of value in treating experimental or clinical cancer. The general state-of-the-art with respect to cancer immunotherapy is examplified in S. K. Carter, "Immunotherapy of Cancer in Man", Am. Scientist, 64, 418-423 (1976); E. C. Holmes, "Immunotherapy of Malignancy in Humans", J.A.M.A., 232(10), 1052-1055 (1975); M. R. Hilleman, "Approaches to Control of Cancer by Immunologic Procedures", Comparative Leukemia Research, pages 105-130 (Pergamon Press 1966); and L. J. Old, "Cancer Immunology", Scientific American, pages 62-79 (May, 1977).
In summary, immunotherapy is regarded today as a secondary form of therapy for cancer, useful only as an adjunct to radiation, surgery and chemotherapy, which comprise the primary modalities for the treatment of cancer. It is well recognized that, in theory, immunotherapy holds great promise for the treatment of cancer, but to date this promise remains unfulfilled.
Accordingly, it is an object of the present invention to provide a method for the immunotherapy of neoplastic disease.
Another object is to provide a new vaccine for use in the immunotherapy of neoplastic disease.
These and other objects of the invention, as well as a fuller understanding of the advantages thereof, can be had by reference to the following description and claims.